The First Army was a field army of the British Army that existed during the First and Second World Wars.
The name First Army was applied to at least two different Australian Army formations during World War II, both of them associated with Lt Gen. John Lavarack. In 1939, the name was used for a "skeleton", Militia formation based at Toowoomba, Queensland and comprised of the 4th Division, 3rd Armoured Division, and the Torres Strait Force.
The German First Army (German: 1.Armee Oberkommando) was a World War I and World War II field army.
The French First Army was a field army of France that fought during World War I and World War II.
The Russian First Army was a World War I Russian field army that fought on the Eastern Front for two years.
The Serbian First Army (СрпÑка Прва Ðрмија / Srpska Prva Armija) was a Serbian field army that fought during World War I.
The Hungarian First Army was a Hungarian field army of World War II.
The Austro-Hungarian First Army was an Austro-Hungarian field army that fought during World War I.
The Italian First Army was an Italian army formation, in World War I, facing Austro-Hungarian and German forces, and in World War II, fighting on the North African front.
The Greek First Army was a Greek field army that fought in Southern Europe during World War II.
The Bulgarian First Army was a Bulgarian field army of World War II.
The Yugoslavian First Army was the first field army of the Kingdom of Yugoslavia during World War II.
The Soviet First Army (also called First Red Banner Army) was a Soviet field army of World War II that served in the Russian Far East.